Conventionally, a felt is used in the press part of a papermaking machine to remove water from a wet paper web. The press part generally comprises a pair of press rolls, or a press roll and a shoe having a surface which conforms with the surface of the press roll. As the felt and wet paper web pass together through the press part, water is transferred to the felt, and thus removed from the wet paper web.
The structure of a conventional press felt is depicted in FIG. 1. The felt 10 comprises a base 20 and a batt layer 30, the base and batt layers being intertwined with each other and thereby integrated. The base 20 is indispensable for imparting strength to the whole felt. An endless woven fabric having a warp and weft is normally used for the base 20.
In the manufacture of the felt 10, an endless, woven base 20, which has almost the same width as the finished felt, is produced in the desired length. Generally, the warp and weft are double woven by a weaving machine to produce an endless base fabric. Alternatively, after weaving a fabric having ends, both ends are sewn together to produce an endless woven fabric. After the base 20 is manufactured, a batt fiber is arranged on the base, and the batt fiber is intertwined with the base by needle punching to produce the finished felt 10.
A felt having the above-described structure needs to be produced in number of different sizes, since the press parts of papermaking machines have various sizes and structures. Weaving base fabrics of various sizes using a weaving machine requires a lot of time and manpower, and it is very difficult to simplify the process and reduce cost.
One approach to solving this problem was a manufacturing method in which a belt-shaped body narrower than the finished felt was first produced, and then wound in a spiral. This approach, which is disclosed in Unexamined PCT National Phase Publication 503385/1994, is illustrated in FIG. 2.
In the approach illustrated in FIG. 2, a belt-shaped body 23 is formed from a thread material selected according to the desired performance of the finished felt. The distance between a pair of guide rolls GR is adjusted according to the desired length of the finished felt. As the guide rolls GR are driven, the belt-shaped body 23 is wound onto both guide rolls. The angle relative to guide rolls GR, at which the belt-shaped body is wound, is adjusted so that the belt-shaped body 23 is wound in a spiral, with the windings in edge-to-edge relationship. The winding operation continues until the total width of the wound belt-shaped body 23 reaches the desired width of the finished felt. Afterward, the adjacent edges of the spiral belt-shaped body 23 are integrally bonded, typically by sewing or by deposition of an adhesive, to produce an endless base 20. Finally, a batt layer is formed on the base 20, to produce the finished papermaking press felt.
A problem with the technology illustrated in FIG. 2 is that, the angle at which a belt-shaped body is wound is not easily controlled. When the angle is incorrect, the sides of the windings may not be in adjacent relationship, making it difficult to carry out the bonding operation. In addition, when the edges of the windings are separate from each other, adequate bond strength may not be obtained. Moreover, the gaps between the windings produce irregularities in the felt surface, which are transferred to a wet paper web in the papermaking process.
The object of the invention is to provide a papermaking press felt which avoids the above-described problems, and which can be manufactured easily and less expensively.